BACKGROUND: Given the pedal variations in biomechanical effects, chronicity, treatment implications, and foot function and alignment in plantar fasciitis, we aim to compare key parameters between individuals with unilateral and bilateral plantar fasciitis. METHODS: Thirty individuals (15 unilateral and 15 bilateral) were included in the study. Static balance was evaluated with the Single-Leg Stance Test, dynamic balance with The Star Balance Excursion Test, gait with OneStep 3.20 mobile software, foot function with The Foot Function Index (FFI), biomechanical alignment with medial longitudinal arch height, Q angle, and lower extremity muscle length, and muscle strength with a Hand-held Dynamometer. RESULTS: The unilateral group exhibited superior performance in unaffected side static and posterolateral dynamic balance (p = 0.037
p = 0.039), and in affected side posterior dynamic balance (p = 0.041). Gait double support asymmetry was better in the unilateral group (p = 0.003). Pain, disability, and activity limitation were more pronounced in the bilateral group (p <
0.05). No significant differences were observed between the groups in medial arch height, Q angle, and muscle shortness/flexibility (p >
0.05). The unilateral group had more strength in the affected side's Gluteus Medius and Adductor muscles (p = 0.046
p = 0.011), as well as in the unaffected side's Quadriceps, Iliopsoas, Gluteus Medius, and Adductor muscles (p = 0.018
p = 0.026
p = 0.006
p = 0.026). CONCLUSION: Balance, foot function and muscle strength were better in individuals with unilateral plantar fasciitis. We think more specific treatments should be included in the management of individuals with bilateral plantar fasciitis aiming to improve balance, foot function and muscle strength.